In ongoing constructions of high-speed and ultra-high-speed communication networks, there are two laying methods for a communication cable which is a medium of such networks: an aerial scheme and underground scheme. The laying of communication cables by an underground scheme is characterized in that it can preserve space environments (appearance of the ground scenery) and is resistant to natural disasters such as earthquakes and typhoons compared to the laying by an aerial scheme. Among underground pipelines, a sewer pipe, in which a branch pipe (a lateral pipe) connecting to the main pipe has already been laid up to each household and the upper part inside the pipe is an open space, particularly has gained attention as an important infrastructure for the FTTH (Fiber To The Home) project in which communication cables are to be drawn to every household.
In order to utilize the open space in the upper part inside the main pipe of such sewer pipes, an information-communicable underground pipe, in which a sheath pipe into which communication cables can be inserted is attached to the upper part of the inner surface of the main pipe at a fixed spacing by means of a support device such as a saddle-type device, is buried in the ground and used as a communication infrastructure.
FIG. 29 is a sectional view of an example of a sewer pipe or the like which is buried in the ground as an information-communicable underground pipe. As shown in the figure, a sheath pipe 103 for inserting a communication cable 106 thereinto is attached to the inner surface of a regular pipe with a bracket 104 or the like, and used as a main pipe 105 of a sewer pipe or the like. To this main pipe 105, branch pipes (not shown), which are connected to each household, are connected. However, these branch pipes have not been constructed as an information-communicable underground pipe information-communicable underground pipe under present circumstances.
There is a disclosure described in JP, A, 11-311369 on an information-communicable underground pipe having a sheath pipe for inserting communication cables thereinto. In this information-communicable underground pipe, by using a sheath pipe support device consisting of: a support plate curved along the outer periphery of the sewer pipe so as to be supported by the upper part of the outer periphery of the sewer pipe; and a bracket having a ring-like shape into which the sheath pipe is passed through and which is attached to the inner side of the support plate so as to protrude into the upper part in the sewer pipe through a through hole provided in the sewer pipe, it is configured such that each bracket of the sheath pipe support device protrudes into the sewer pipe from each through hole which is provided in the upper part inside the sewer pipe at a proper spacing along the pipe axis direction, and the sheath pipe, which is attached in such a way that each through hole is water tightly covered with each support plate and is disposed along the pipe axis of the sewer pipe, is inserted into a bracket of each sheath pipe support device thereby being supported. Such configuration makes it possible to support a sheath pipe into which communication cables are inserted in the upper part inside the sewer pipe with a small occupying area. Moreover, since the sheath pipe is supported in the upper part in the sewer pipe, there is no risk that the flow capacity of sewage in the sewer pipe is reduced, and the workability at the installation site of the sewer pipe is significantly improved by attaching the sheath pipe to the sewer pipe in advance.
However, before the concept of the information-communicable underground pipe is created, an ordinary pipe without a sheath pipe was used as a sewer pipe or the like. Therefore, in the above described information-communicable underground pipe, it was necessary to attach the sheath pipe support device by digging up the upper part of the outer periphery of the sewer pipe buried in the ground to provide a through-hole therethrough. Also needed was an operation such as digging out a pipe having no sheath pipe to remove and replace it with an information-communicable underground pipe in which a sheath pipe is attached by means of a sheath pipe support device or a saddle-type device.
Thus, to convert a regular conduit having no sheath pipe into an information-communicable underground pipe, a very large scale operation was needed, and therefore there was a growing demand for converting a regular pipe having no sheath pipe into an information-communicable underground pipe by easily attaching a sheath pipe thereon.
Further, to lay communication cables up to each household through a branch pipe which is branched off from the main pipe of a sewer pipe, the laying path was too complicated and further the inner diameter of the branch pipe was too small and branched at various angles from the main pipe through a branch pipe opening. From these reasons, such laying is in reality not performed since there are technical difficulties compared with the case in which communication cables are laid in a straight fashion in the main pipe. Other technical difficulties in laying communication cables in a branch pipe exist in that the communication cable must be laid without impairing essential functions used as a lifeline, in that the communication cable must have water resistance, chemical resistance, anti-rat property, that is, resistance to breakages due to rat-bites, and anti-high-pressure-cleaning property, that is, resistance to high-pressure cleaning for checkup of the conduit.